Recently, a time synchronous communication network has been used for an on-vehicle network which communicates among a plurality of on-vehicle electronics devices equipped on a vehicle in order to secure real-time process of communication. One of the examples of methods for the time synchronous communication is FlexRay. In FlexRay, one cycle of communication is referred to as a communication cycle. The communication cycle includes a plurality of slots and is previously assigned to each controller on a network. Each controller executes a transmission process of a frame or a reception process of a frame among assigned slots.
FIG. 1 is a schematic block diagram showing an on-vehicle network and controllers using a time synchronous communication network. As shown in FIG. 1, each of controllers 1, 2 is connected to a network (a network bus) and mainly includes a processor 11, a memory 12 and a communication control device 13. The communication control device 13 counts communication cycles and stores in a communication cycle counter 14. Each communication control device 13 in the controller 1 and the controller 2 exchanges the communication cycle 1004 among the communication control devices and controls the communication cycle 1004 to constantly keep the same value. A slot counter 18 is incremented from 0 at the starting time of the communication cycle.
A filtering condition 17 determines a condition of the communication cycle and the slot value when a frame transmission and frame reception are executed. In the frame transmission, the communication control device 13 transmits frames in which the communication cycle is matched with the slot value based on a filtering condition 17 from a transmission buffer 15 assigned to each frame. In the frame reception, the communication control device 13 receives the frames in which the communication cycle is matched with the slot value based on a filtering condition 17 from a network 3 and stores the frames in a reception buffer 16 which is statically assigned to each frame.
FIG. 14 shows an example of slot assignment when frame A and frame C are transmitted in a cycle from the controller 1 to the controller 2. A cycle length of the communication cycle is set to 10 msec (a length of the communication cycle counter), and a communication cycle of each frame is set to 20 msec (which is 2 when converted to the communication cycle counter). As shown in FIG. 14, when a filtering condition 17 of frame A is set to “communication cycle=2N (N is a number from 0 to 31)” and a filtering condition 17 of frame C is set to “communication cycle=2N+1 (N is a number from 0 to 31)”, frame A and C can be transmitted and received using the same slot.
As described above, the time synchronous communication, which executes the frame transmission and the frame reception in synchronization with the communication cycle and the slot, does not generate competition on the network. As a result, bandwidths of the network can be used effectively.